Rectifier system



Patented Sept. 5, 1939 UNITED STATES PATENT GFFICE RECTIFIER SYSTEM Application April 12,

2 Claims.

My present invention relates to rectier systems generally, and especially to detecting arrangements for carrier wave communication systems.

The object of the present invention is to provide a detector circuit whose eciency decreases as the signal voltage impressed thereon increases beyond a normal value.

A particular object is to provide a detector circuit, for a high frequency signal system, that possesses a marked saturation characteristic whereby the deleterious effects of intermittent interfering voltages having amplitudes relatively high as compared with desired signals are minimized.

A further object is to provide a detecting system whose output varies relatively little with the strength of signals applied thereto, thus producing a type of automatic control more suitable for telegraphic code reception than the usual automatic Volume control arrangement which controls the ampliiication of the receiver in accordance with the strength of the carrier wave, since in code signalling there is no continuous carrier.

In the drawing:

Fig. l shows a detector system employing a triode tube whose plate-cathode circuit is used as a diode detector, while its grid is used to control the internal resistance of the detector.

Fig. 2 shows an alternative form of the invention wherein a multi-electrode tube is employed.

Referring specifically to Fig. 1, signalling voltages are impressed on primary coil L1 of transformer L1--L2 from a source V which may be the output of a radio frequency amplifier whose input is energized from a signal collector, such as an antenna. In the case of a superheterodyne receiver, V would represent the output of the intermediate frequency amplifier. Secondary coil L2 may be tuned, if desired, by variable condenser C2. Voltage taken from across a suitable portion of coil L2 is impressed in series with radio frequency icy-pass condenser C between anode A and cathode K of triode detector D whose cathode may be grounded, as shown by the ground symbol, if desired. A high resistance R is connected in shunt to condenser C, and the grid G is connected adjustably to R. Audio frequency output voltage is taken from across R and impressed, in some cases through blocking condenser C3, upon a utilization circuit as indicated by the legend. Finally, a source B of direct voltage has its negative terminal connected to cathode K and its positive terminal connected through a high resistance R1 to the junction of R and Lz. In the 1938, Serial N0. 201,523

(Cl. Z50- 27) absence of incoming signals source B maintains the potentials of anode A and grid G more positive than that of cathode K, whose potential will hereafter be assumed as zero, so that the detector is highly sensitive for the reception of weak signals. If, however, sufficiently strong signals are applied, anode A assumes a negative potential, thus causing grid G to become negative by an amount dependent upon the position of its connection to R. If the ampliiication factor of the tube is large and if the grid G is connected at or near the most negative end of R, a relatively enormous increase in applied signal Voltage is required to cause any considerable further increase in rectiiied current, since the instantaneous plate potential must swing positive by an amount equal to the negative potential of the grid multiplied by the amplication constant of the tube in order for the plate A to draw any current at all, whereas in the range of normal signals or weak signals, that is to say in the range of signals in which the grid is positive, anode current flows whenever any signal voltage at all is applied to the anode.

It will be seen that the magnitude of the limiting action thus described may be controlled by adjustment of the position of the connection of grid G to R, the limiting action being maximum when this connection is made to the end of R which is remote from the cathode. Furthermore, the signal strength beyond which limiting action begins may be increased by increasing the voltage of the source B. Resistances R and R1 should always be suiiiciently high to permit good detecting action but subject to this condition their ratio may be altered for the purpose of adjusting the incidence of limiting action since their ratio also affects the potential of the anode in the absence of signals.

Fig. 2 shows a modification of the invention wherein a tube is used which has a screen grid maintained at a positive potential and located between the control grid G and the anode A. A suppressor grid located between the screen and plate may also be employed if desired, or a multiplicity of positive grids may be used in place of the single screen grid shown. The essential feature of Fig. 2 is that the existence of a positive potential on the screen makes it possible for the anode A to draw electrons to itself whenever any signal input is applied unless the grid G is made negative by more than a predetermined amount which depends upon the potential of the screen and geometry of the tube.

It will be seen that the connections employed in Fig. 2 are the same as those in Fig. 1, except that resistor` R1 of Fig. 1 is not required in the modification shown in Fig. 2, while the source B of direct voltage has its positive terminal connected in Fig. 2 to screen grid S and not to control grid G as was the case in Fig. 1. The operation of Fig. 2 is similar to that of Fig. 1 in that strong signals produce a negative potential on grid G, thus reducingthe amount of current that can be drawn to the anode. With a well screened tube, for instance a tube having a series of screen grids one behind the other, there is `*a Well defined cut-01T value of control grid bias for a given screen potential beyond which bias substantially no anode current is produced by any applied anode potential. Hence the detector output across R has as its upper limit of potential, the cut-off value, if the control grid G is connected to the end of R remote from the cathode so as to receive the full direct voltage output of the detector. As the control grid connection to R is moved towards the cathode the limiting action is decreased.

It will be noted that radio frequency voltage has been assumed to be absent from control grid G in both of the figures. If condenser C is not suiiciently large vto by-pass radio frequency voltage completely enough for the proper operation of the circuit, it is a simple matter for one skilled in the art to interpose between grid G and its connection to R a resistance-capacity filter that will permit only direct voltage or slowly varying voltage to reach the grid G.

While I have shown and described in some detail two arrangements embodying my invention, I do not intend that the scope of my invention shall be limited except in accordance with the.

following claims.

What is claimed is:

l. A rectifying system for alternating currents comprising in combination a space current discharge tube including a cathode, an anode and a control grid, a source of alternating voltage and connections for applying alternating voltage derived from said source to a circuit including said cathode and anode, a load circuit including resistance arranged to be traversed by rectied current flowing between said anode and cathode external to said tube, connections for impressing between said grid and cathode at least a portion between the cathode and anode, a load impedance bypassed for radio currents in circuit with the cathode and anode for developing a rectified voltage from rectied radio currents, means con'- necting said grid to a point on the impedance such that said anode and said grid are at a common direct current potential in the absence of impressed waves while the lgrid assumes .a negal tive potential with respect to the cathode in the presence of waves, means establishing said screen .grid at a positive potential with respect to the cathode, anode and control grid'thereby to provide a Well dened cut-off value of control grid bias.

' ROY A. WEAGANT. 

